This invention relates generally to a mobile temperature-controlled container for transporting perishable cargo and, more particularly, to distribution of temperature-controlled air through out the cargo space defined within the container.
Temperature-controlled containers are commonly used for shipping perishable cargo, such as fresh produce, seafood and the other foods that must be maintained during transit at a temperature within a specified temperature range. Containers of this type are typically designed to accommodate transport by land on trailers, by sea on container ships, by rail on flat-bed train cars and even by air in cargo planes. Such versatile containers are commonly referred to as intermodal containers.
In conventional industry practice, temperature controlled containers are equipped with a refrigeration unit that is secured to one wall of the container, typically the front wall of the container. The refrigeration unit includes a compressor, a compressor motor, and a condenser unit isolated from the cargo space, and an evaporator unit operatively associated with the cargo space defined within the container. The condenser unit includes a refrigerant heat rejection heat exchanger and a condenser fan that draws ambient outdoor air through the condenser heat exchanger and discharges that air back into the outdoor environment. The evaporator unit includes a refrigerant heat absorption heat exchanger and one or more, typically two, evaporator fans which draw return air from the cargo space defined within the container through the evaporator heat exchanger for temperature conditioning and delivers that conditioned supply air back into the cargo space defined within the container. Although the refrigeration unit is typically operated in cooling mode to reduced the temperature of the return air, the refrigeration unit may be equipped with an auxiliary air heating device for heating the return air when the container is in transit in a region having an environment wherein the ambient outdoor temperature is below the desired temperature range in which the cargo in transit must be maintained.
The cargo space of the transport cargo container constitutes the volume defined between the front wall, the rear wall, the opposed side walls, the floor and the ceiling of the container structure. The cargo is stacked within the cargo space, generally on pallets, disposed atop the floor of the container. In standard practice in the industry, the floor of the container is formed of a plurality of parallel, longitudinally extending T-bars supported. The T-bars are spaced apart laterally to form a series of longitudinally extending air passageways that are open to the cargo space above the floor. A portion of the temperature-controlled air discharging from the evaporator passes downwardly along the front wall of the container and into these passageways. As the air flows along the passageways towards the rear wall of the container, air passes from the longitudinally directed airflow upwardly into the cargo space. Additional conditioned air discharges downwardly out of side outlets to flow along the floor adjacent each of side wall toward the rear wall. As this air flows toward the rear wall of the container, most of the air passes upwardly along the bounding side wall of the container. The air that reaches the rear wall passes upwardly along the rear wall and is then drawn forwardly above the stacked cargo toward and into a return air inlet chamber extending along the upper portion of the front wall. The air that flows upwardly along the side walls and the air passing upwardly from the floor through the stacked cargo is entrained in the forwardly flowing air above the cargo space and drawn into the return air inlet chamber. Cargo containers having floors of this general construction are shown, for example, in U.S. Pat. Nos. 5,830,057; 6,923,111; and 7,266,961.
Cargo containers of this type typically have a length of approximately twenty or forty feet (about 6.12 to 12.2 meters) in length, a height of about nine and one-half feet (about 2.9 meters), and a width of about eight feet (about 2.44 meters). Consequently, delivering adequate conditioned air from the front of the container where the air discharges from the evaporator of the refrigeration unit to the rear of the container is problematic. Inherently, air flowing through the passageways defined by the T-bar floor tends to passes upwardly into the cargo space through the openings between adjacent T-bars disproportionately. That is, there is a natural tendency for more conditioned air to pass from the passageways upwardly into the cargo space at the forward end of the container with the upward flow of air getting progressively smaller as the air flow progresses from front to rear longitudinally along the length of the container. This maldistribution of conditioned air is further complicated when cargo is not relatively tightly stacked as more air will tend to pass through gaps between cargo stacks as these gaps represent a path of low resistance. While various techniques have been tried to increase the “throw” of the rearwardly flowing air so as to improve the reach of the conditioned air to the rearwardly stowed cargo, in conventional temperature-controlled cargo containers, providing adequate flow of conditioned air to the rearward regions of the container, including the upper corners of the cargo space near the rear wall of the container, remains problematic. In general, in conventional temperature-controlled containers having floors of conventional T-bar construction, the stowed cargo tends to be overcooled at the end of the cargo space adjacent the refrigeration unit and undercooled at the door end of the container.